Protease-Activated Receptor-2 Plays a Critical Role in Vascular Inflammation and Atherosclerosis in Apolipoprotein E-Deficient Mice.

BACKGROUND: The coagulation system is closely linked with vascular inflammation, although the underlying mechanisms are still obscure. Recent studies show that protease-activated receptor (PAR)-2, a major receptor of activated factor X, is expressed in both vascular cells and leukocytes, suggesting that PAR-2 may contribute to the pathogenesis of inflammatory diseases. Here we investigated the role of PAR-2 in vascular inflammation and atherogenesis. METHODS: We generated apolipoprotein E-deficient ( ApoE-/-) mice lacking systemic PAR-2 expression ( PAR-2-/- ApoE-/-). ApoE-/- mice, which lack or express PAR-2 only in bone marrow (BM) cells, were also generated by BM transplantation. Atherosclerotic lesions were investigated after 20 weeks on a Western-type diet by histological analyses, quantitative reverse transcription polymerase chain reaction, and Western blotting. In vitro experiments using BM-derived macrophages were performed to confirm the proinflammatory roles of PAR-2. The association between plasma activated factor X level and the severity of coronary atherosclerosis was also examined in humans who underwent coronary intervention. RESULTS: PAR-2-/- ApoE-/- mice showed reduced atherosclerotic lesions in the aortic arch ( P<0.05) along with features of stabilized atherosclerotic plaques, such as less lipid deposition ( P<0.05), collagen loss ( P<0.01), macrophage accumulation ( P<0.05), and inflammatory molecule expression ( P<0.05) compared with ApoE-/- mice. Systemic PAR2 deletion in ApoE-/-mice significantly decreased the expression of inflammatory molecules in the aorta. The results of BM transplantation experiments demonstrated that PAR-2 in hematopoietic cells contributed to atherogenesis in ApoE-/- mice. PAR-2 deletion did not alter metabolic parameters. In vitro experiments demonstrated that activated factor X or a specific peptide agonist of PAR-2 significantly increased the expression of inflammatory molecules and lipid uptake in BM-derived macrophages from wild-type mice compared with those from PAR-2-deficient mice. Activation of nuclear factor-κB signaling was involved in PAR-2-associated vascular inflammation and macrophage activation. In humans who underwent coronary intervention, plasma activated factor X level independently correlated with the severity of coronary atherosclerosis as determined by Gensini score ( P<0.05) and plaque volume ( P<0.01). CONCLUSIONS: PAR-2 signaling activates macrophages and promotes vascular inflammation, increasing atherosclerosis in ApoE-/- mice. This signaling pathway may also participate in atherogenesis in humans.

Obesity-induced DNA released from adipocytes stimulates chronic adipose tissue inflammation and insulin resistance.

Obesity stimulates chronic inflammation in adipose tissue, which is associated with insulin resistance, although the underlying mechanism remains largely unknown. Here we showed that obesity-related adipocyte degeneration causes release of cell-free DNA (cfDNA), which promotes macrophage accumulation in adipose tissue via Toll-like receptor 9 (TLR9), originally known as a sensor of exogenous DNA fragments. Fat-fed obese wild-type mice showed increased release of cfDNA, as determined by the concentrations of single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) in plasma. cfDNA released from degenerated adipocytes promoted monocyte chemoattractant protein-1 (MCP-1) expression in wild-type macrophages, but not in TLR9-deficient (Tlr9 (-/-) ) macrophages. Fat-fed Tlr9 (-/-) mice demonstrated reduced macrophage accumulation and inflammation in adipose tissue and better insulin sensitivity compared with wild-type mice, whereas bone marrow reconstitution with wild-type bone marrow restored the attenuation of insulin resistance observed in fat-fed Tlr9 (-/-) mice. Administration of a TLR9 inhibitory oligonucleotide to fat-fed wild-type mice reduced the accumulation of macrophages in adipose tissue and improved insulin resistance. Furthermore, in humans, plasma ssDNA level was significantly higher in patients with computed tomography-determined visceral obesity and was associated with homeostasis model assessment of insulin resistance (HOMA-IR), which is the index of insulin resistance. Our study may provide a novel mechanism for the development of sterile inflammation in adipose tissue and a potential therapeutic target for insulin resistance.